Recording information with a watermark related to a prerecorded medium mark on an information carrier

ABSTRACT

A system for copy protection of recorded information is disclosed, including an information carrier, a recorder and a player. The information carrier, e.g. an optical disc, includes a medium mark representing a first bitpattern, which medium mark cannot be copied on standard recording devices. The recorded information includes a watermark representing a second bitpattern, which second bitpattern has a predefined relationship to the first bitpattern. The watermark cannot be manipulated without disturbing the quality of the reproduction of the information. The relationship, preferably a one-way function, between the watermark and the medium mark requires that an illegal copy also has the corresponding medium mark. As neither the watermark nor the medium mark can be manipulated, a strong protection against illegal copying is achieved. The recorder includes encoder means for embedding the watermark in the information and generator means for generating the second bitpattern according to said relationship. The player includes verification means for verifying said relationship.

FIELD OF THE INVENTION

The invention relates to the copy protection for recorded media.

BACKGROUND OF THE INVENTION

The invention relates to a system for copy protection of recordedinformation, includes an information carrier having a medium markrepresenting a first bitpattern, a recorder for recording theinformation on the information carrier and a player for reproducing therecorder information from the information carrier.

The invention further relates to a recorder for recording information onan information carrier with a medium mark representing a bitpattern.

The invention further relates to an information carrier with recordedinformation and a medium mark representing a bitpattern.

The invention further relates to a player for reproducing informationfrom an information carrier and the system including for detecting amedium mark representing a bitpattern.

Copy protection has a long history in audio publishing. The presentlyinstalled base of equipment, including PC's with audio cards, providelittle protection against unauthorized copying. In any copy-protectionscheme, the most difficult issue is that a pirate can always attempt toplayback an original disc, he can treat the content as if it were ananalog home recording and record this. Consumer recorders should be ableto copy recordings of consumer's own creative productions without anylimitation, but prohibit the recording of copy-right material. Thus, thecopy protection mechanism must be able to distinguish between consumers'own creations and content that originates from professional musicpublishers. The equipment must make this distinction based on thecontent only, as any reference to the physical source of content (e.g.disc or microphone) is unrealiable. For digital storage media such asDCC, “copy bits” have been defined, which bits indicate a copyrightstatus, e.g. “no copy allowed”, “free copy” or “one generation of copyallowed”. Other copy bits may indicate that the medium storing theinformation must be a “professional” medium manufactured by pressing andnot a “recordable” disc.

A system for copy protection of recorded information comprising arecorder, information carrier and player, is known from EP-0545472corresponding to U.S. Pat. No. 5,724,327 to Timmermans et al. (listed asdocument D1 below). The copy protection is based on a so-called mediummark, i.e. a physical mark representing a bitpattern indicating thestatus of the medium, e.g. a code indicating a “professional” diskmanufactured by pressing. A medium mark should not be copyable orchangeable by standard recording equipment, and therefore it is to bestored on the information carrier in a manner different from therecorded information, such as audio or video. The medium mark isdetected by the player and if it is not present or indicates a differentstatus (e.g. “recordable disc” on an illegal copy), reproduction isblocked. The known information carrier has a prearranged guiding track,a so-called pregroove. In the track determined by the pregroove,information can be written in a predefined manner represented byoptically readable patterns which are formed by variation of a firstphysical parameter, such as the height of the scanned surface. Thepregroove has variations in a second physical parameter, such as anexcursion in a transverse direction, also denoted as wobble. The wobbleis FM modulated and this modulation represents a bitpattern which isused for recovering the information, e.g. a descramble code forrecovering information stored as scrambled information. The bitpatternconstitutes a medium mark, because the track wobble cannot be copied toa recordable disc on standard recording equipment. The known playerincludes a reader for reading the optical patterns and recoveringapparatus for recovering the bitpattern from the medium mark. The playerand information carrier form a system for controlled informationreproduction. For this purpose, the player has apparatus for controllingthe reproducing of the information depending on the medium mark. If theinformation is copied on a writable information carrier, the informationof this copy will not be reproduced by a player, because during thewriting process only the optical patterns are written in the predefinedmanner and the copy itself does not contain any medium mark.

Those skilled in the art are referred to the following documents:

-   -   (D1) EP-0545472—corresponding to U.S. Pat. No. 5,724,327 to        Timmermans et al. regarding Closed information system with        physical copy protection    -   (D2) WO 97/13248-A1—corresponding to U.S. application Ser. No.        08/723,653 filed Oct. 3,1996 by Linhartz regarding Watermarking        encoded signals.    -   (D3) EP-A 97200197.8 filing date 27 Jan. 1997—corresponding to        U.S. application Ser. No. 09/013,540 filed Jan. 26, 1998        regarding Watermarking of Bitstream- or DSD-signals by A. A. M.        Bruekers et al.    -   (D4) U.S. Pat. No. 5,649,054 to Ooman et al. issued Jul. 15,        1997    -   (D5) WO IB97/01156 corresponding to U.S. application Ser. No.        08/937,435 filed Sep. 25, 1997 regarding Lossless coding for DVD        audio A. A. M. Bruekers et al.    -   (D6) “New Directions in Cryptography” by Diffie and Hellman,        IEEE Transactions on information theory, Vol IT-22, No. 6,        November 1976, p. 644–654

The above references are hereby incorporated herein in whole byreference.

SUMMARY OF THE INVENTION

The inventors recognize a problem in the known system. The problem isthat copying the information after reproduction cannot be sufficientlycontrolled. If the information includes the copy bits, such bits can bemanipulated easily, e.g. on a PC or in a small electronic circuit. Theinformation with the manipulated bits can be copied freely. If theinformation is recorded in a scrambled way and de-scrambled duringreproduction using the medium mark bitpattern, the information can berecorded in its plain (descrambled) status and is not protected againstcopying at all.

It is an object of the invention to provide a system in which copying isbetter controlled and the copy protection cannot be circumvented bysimple manipulation of the copy bits.

For this purpose, in the system according to the invention, the recordedinformation includes a watermark representing a second bitpattern. Thesecond bitpattern has a predefined relationship to the first bitpattern,and the recorder includes an encoder for embedding the watermark in theinformation and a generator for generating the second bitpatternaccording to the predefined relationship between the first and thesecond bitpattern. The player also includes a verifier for verifying therelationship between the second bitpattern and the first bitpattern. Thewatermark is indicative of the copyright status of the recordedinformation. This has the advantage, that a signal representing theinformation after reproduction still contains the watermark and arecorder can be aware of the copyright status of the signal offered forcopying, whereas the copyright status of the signal indicated by thewatermark cannot be changed or manipulated without disturbing thesignal. The prior art system using the medium mark as a descramble keyor a fixed code is vulnerable to an ‘illegal’ recordable disc have afixed, false medium mark. For example, any information read from ascrambled copy protected disc can be recorded on an illegal copy after(re-)scrambling using the fixed, false key. The relation between thewatermark bitpattern and the medium mark bitpattern requires that themedium mark bit correlates with the recorded information. Hence in thesystem according to the invention a fixed, false medium mark cannot beused to make illegal copies. As there is a predefined relation definedbetween the first (medium) bitpattern and the second (watermark) markbitpattern, a strong copy protection is realized, because an illegalcopy must contain the specific medium mark correlated to the watermarkaccording to the predefined relation and therefore the malicious partyis forced to obtain the relation for manipulation. Choosing a suitablerelation can create a barrier against such manipulation. The detectionof the watermark in the player is relatively simple and the informationread from the information carrier does not require any processing, suchas descrambling. Verification in the player of the watermark bitpatternagainst the medium mark is a strong protection against copying, asneither of the marks can be easily manipulated. A further advantage is,that the verification function in the player can be relatively slow, asthe verification of the predefined relationship needs to be performedonly once when starting the reproduction of the recorded information.

It is to be noted, that WO 97/13248-A1, which is filed before butpublished after the priority date of this invention (PHN 15391, documentD2 listed above) describes a watermarking system for a video signal. Thewatermarked video signal is recorded on a disk containing a medium mark.However the medium mark only indicates the type of medium and has nocorrelation with the signal or the watermark.

In a preferred embodiment of the system, the relationship includes acryptographic one-way function. The one-way function prevents, when therequired result (e.g. the watermark bitpattern) is known, that thesource (e.g. the medium mark bitpattern) can be found by calculating‘backwards’. This has the advantage, that the malicious party is forcedto obtain the medium mark bitpattern directly from the original medium.The original medium may not be available to him or the player may beequipped not to make the medium mark bitpattern externally available.This creates a significant barrier for the malicious party trying tomake an illegal copy with a “chinese” copy of the medium mark.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter andwith reference to the accompanying drawings, in which

FIG. 1 shows conditional playback rules,

FIG. 2 shows a copy protection system with a recorder, informationcarrier and player,

FIG. 3 shows a one-way function,

FIG. 4 shows a recorder, and

FIG. 5 shows a player.

We propose a copy control method for bitstream- or DSD-signals (DirectStream Digital) stored on storage media such as DVD audio (DigitalVersatile Disc). The method relies on a watermarking method, such as theone proposed by A. A. M. Bruekers et al, in document D3 listed above.Recently, it has been realized that watermarks or embedded signallingcan be used to make copy protection methods more robust against attacks.Embedded signaling or watermarking is a method of burying information inthe audio content. In this text we use the word professional for anyproduct that is officially registered with a trusted party whichrepresents the interests of the recording industry and hardwaremanufacturers. We denote any other product as a consumer product.Consumer products are assumed to obey copyright rules, enforced eitherby a patent licensing agreement or by law, or both.

For Copy Protection a total solution is needed. Watermarking is notrestricted to digital formats, but can also be embedded and detected inanalog signals. Often, spread-spectrum technology is proposed forembedding watermarks into audio. A technical difficulty ofspread-spectrum methods is that retrieval or detection of such embeddeddata requires substantial signal processing. Although this is not aproblem for professional equipment used in legal cases to prove theorigin of the audio material, the computational effort appears farbeyond what is feasible and economically reasonable within consumerelectronic products to support copy protection. A particular problem isthat the audio quality requirements set by the music industry wouldrequire such large spreading gains that synchronization and datadetection would take excessively long integration times. Parametersconsidered in spread spectrum watermarking presumably do not satisfycurrent audio quality requirements. Future standards aim at furtherenhancing the audio quality and simultaneously require secure protectionof music IPR. It is our strong belief that it is unlikely thatsatisfactory methods will indeed be found in near future to combinethese two requirements at reasonable cost. Particularly, the absence ofprotective measures in the installed base of audio equipment causes aproblem. It appears virtually impossible to avoid that signals can becopied by going back to analog. Moreover, consumer expectations are thatsome kind of home taping, e.g. to listen in the car, should be possible.On top of that, some countries levy a fee on blank tape for analogcopying for private use, and certain technical means to restrict analogcopying are not legally acceptable. There appears an opportunity to setnew standards for storage and representation of digital audio (e.g.DVD), but technology to solve the copy protection issue completely(i.e., including analog copying) is unlikely to become available soon.For audio, a bitstream-only solution may be of use. Given thissituation, it can be useful to protect new audio storage media againstunauthorized copying of discs, even if analog copying remains possible.In order to copy, conversion into other domains (e.g. analog) are neededand some loss of quality occurs. The scheme proposed here using digitalwatermarking does not solve the existing problem of piracy and excessivehome taping whereby the audio signal is converted to analog as part ofthe copy process. If the industry adopts a copy protection scheme basedon watermarking, it will presumably come to a layered approach. The mostrobust watermark should withstand D/A and A/D conversion, but this willrequire long integration times for the detection. This implies that therecord or playback inhibit decision will be delayed. A watermark in thebitstream can be detected within milliseconds and trigger copyprotective measures immediately. Such fast detection appears essentialif bitstream signals are transferred over open busses (such as P 1394).In summary, the method described in this document has the followingproperties:

-   -   Bitstream or DSD signals with copy-right restrictions can        immediately be distinguished from home recordings.    -   Traceability of the professional or consumer recorder.    -   It can co-exist with other methods that also protect against        other forms of copying (e.g. analog). In particular, it appears        of interest to add conditional playback using the method        proposed here to a conditional recording method which also        checks for spread spectrum watermarks.

In the invention we propose a scheme that protects against direct(bitwise) copying of high quality digital DSD streams. The method doesnot technically protect against conversion of DSD to PCM or analogue.However, some protection is provided against such attacks in the sensethat if a bitstream/DSD signal, it is converted back into DSD may bewatermarked with the serial number of the consumer DSD encoder. Themethod relies on a watermarking method, such as the one proposed by A.A. M. Bruekers et al. Our method can coexist with many other forms ofcopy protection, including serial copy management bits and the embeddedsignaling of spread spectrum watermarking. The additional hardware inconsumer equipment appears very small. Another tool used in the systemembodiment is a medium mark, i.e. a method to distinguish aprofessionally mastered disc from a recordable. Implementations of suchtool can be a wobble key (as known from document D1 above), modulationof channel code errors (e.g. EFM) or intentional modulation the jitterof pits and lands of a disc, or embedding an on-disc chip, or just datawritten in the lead-in area which is not accessible by consumerrecorders. These two tools (watermark and medium mark) are used tosupport the following features (both or just one):

-   -   Conditional recording is the most commonly known method for copy        protection. A consumer recorder will not record material unless        it sure that the material may indeed be copied legally.    -   Conditional playback, on the other hand, accepts that some        people will be able to get the bits of copy-righted DSD on a        pirate disc anyhow.

Conditional playback will make sure that such a pirate disc can notplayback on consumer players. That is, pirates cannot commerciallydistribute illegal copies. In conditional playback, a consumer DVD audioplayer will only play audio discs if certain copyright conditions aremet. The player identifies the audio content either as a consumerrecording or as professionally published audio content, by detecting orchecking for a watermark in the audio stream. In the latter case(professional content protected by copyright), the player checks whetherthe physical disc is original and professionally mastered, rather than acopy on a consumer recorder or consumer disc press. This requires both amarking method for the content (watermarking) and a method for markingthe physical storage medium that can only be produced by a professionalrecorder or pressing machine.

FIG. 1 shows schematically the conditional playback rules embedded inthe consumer player, which are applied after a watermark has beendetected. As a first check 11 the presence of the medium mark, usually aphysical mark, is detected by the reading head in a manner differentfrom reading recorded information, e.g. by demodulation of the wobble.If the medium mark is present it is verified to be a valid professionaldisc mark at a second check 16, and if so playing 17 is enabled if thewatermark and the medium mark correlate according to a predefinedrelation. If the medium mark is not present or indicates a consumerrecorded disc (checked in a third check 12), the watermark is decoded indecoder 13. The watermark may be indicative for free-to-copy (audio)information, and then playing 14 of the disc is enabled. If thewatermark is indicative for copy-protected information, the playingaction is blocked in state 15.

In a first embodiment of the system professionally mastered audio discscarry an identifier unique to the publisher, which can not be copied.This identifier can for instance be a set of bits written in an areathat is not accessible for recorders, it can be a wobble key or aspecial pattern in the running DC component of the EFMplus channelcodeused in DVD. The DVD audio player checks for this mark. If this mark isunavailable or if it contains a special code reserved for home discrecorders, it will only playback the DSD stream if a special watermarkis found that identifies the DSD encoder. If this watermark is notfound, as would be the case if a professionally released audio stream iscopied illegally to a recordable disc, the audio is not played back atall. To avoid any degradation of the quality of professional DSDreleases this scenario does not require that the audio content ofprofessionally released audio titles is watermarked, but this scenariorequires that the watermark embedding method is used in consumerequipment. Besides a frequently repeated copy control bit, a uniqueserial number is embedded into the audio stream by all DSDencoders/recorders in the consumer market. The circuitry to embed thisnumber appears simple. The consumer can not copy professional DSD audiodirectly to a DVD audio disc, as it will not playback (because of thewatermark be absent). If he converts the signal to analog, PCM oranother format, and then re-creates DSD, the particular DSD recorder canbe traced. Moreover, the scheme can be defined in such a way that homerecordings have smaller dynamic range. A further strengthening isachieved if each player not only checks whether a watermark is presenton consumer discs, but also check whether a valid serial number isembedded. Known cryptographic methods can be used for integrity checks,e.g. concatenating a digital signature to the serial number. This avoidsthat a pirate can tamper with serial numbers.

A second embodiment is similar to the first, but the bit stream ofprofessionally released audio does also contain a watermark. Thiswatermark is used to verify the medium mark in a cryptographic way. Themedium mark now differs from title to title. The relation between thebitpattern represented by the watermark and the bitpattern representedby the medium mark is not easy to manipulate. Preferably, thecrytographic relation is chosen as follows. Let y=F(x) and x=G(u) be twocryptographic one-way functions, i.e. their inverse is computationallyinfeasible to compute with finite arithmetic resources. This scenariouses a seed u to create x and y, according to x=G(u) and y=F(x)=F(G(u)).In this concept G and F may be the same function, but this is notnecessary. On a professionally mastered disc, the embedded watermarkcontains y and the medium mark carries x. Professional recorders alwaysperform the G function before writing a medium mark. That is, they embeda medium mark x which is internally generated from the user input u. All(consumer) players perform F to verify the medium mark if a watermark isfound that indicates that the content is copy protected. Consumerrecorders are assumed not to be able to write a medium mark at all.Using the system the copy-right owner can decide himself whether or notto release the seed u, which allows copying. In professional musicpublishing, it can be necessary to create a tape master of the musictitle. The audio is then pre-encoded with embedded the watermark y.During the production process, the professional recorder (disc mastergenerator machine) directly accepts the watermarked DSD 30 and insertsthis after the DSD encoder/watermarker 23 of FIG. 2. Seed u 22 is alsoinserted during this process. This also provides some protection if themaster tape is stolen, but u is not compromised. Preferably, therecorder checks the watermark against us and x (as described with FIG.4, conditional recording).

FIG. 2 shows a copy protection system with a recorder, informationcarrier and player. The Professional Recorder has an audio input 21 to aDSD encoder 23, which also embeds the watermark bitpattern y in thebitstream 30 to be recorded on the master disc 26. The watermarkbitpattern y is available on the output of generator 25, which hasbitpattern x to be represented by the medium mark 20 on its input. Themedium mark 20 is created on the master disc 26. Preferably thebitpattern x is generated by a generator 24 from the input seed u on theinput 22. The master disc 26 is multiplied by the usual manufacturingmethods to copy protected information carriers 27, which are to beplayed in the consumer player 28. The consumer player has a verifier 29,which compares the detected watermark bitpattern y with a calculatedvalue y′, which is based on the detected bitpattern x from the mediummark.

In this scenario, a pirate must have access to a professional recorderto create media marks on a pirate disc. A pirate can copy the audio andrecover y, but he cannot calculate x. This system adds security to thecopy protection scheme, particularly if we can ensure that x cannoteasily be read from the disc, i.e., remains within the first chip in thebasic engine (that must use x to verify watermark y). Moreover, even ifa pirate can read x, he must find u to enter it into the recorder and tohave x written as a medium mark. No recorder will directly accept to xand write it to disc. In this scenario, a pirate must physically modifyboth his (officially registered mastering) recorder (to bypass the Gfunction) and his player (to extract x).

In a further embodiment copy protection can be provided for consumerrecordings. It can be envisioned that consumers want to publish ordisseminate their own recorded audio creations at a small scale. We nowdescribe how consumer recorders can implement some of the elements ofthe above scheme. This gives consumers the possibility to create discsthat can only be copied directly (bit-by-bit) if the recipient alsoknows seed u. Part of the medium mark must be recordable by therecipient. A possible embodiment is to split x into two parts, withx=x₁||x₂, such that y=F(x₁||x₂). Then x₁ acts as a medium mark, similarto the scenario described above, and x₂ is written as a separate file onthe disc. Professional recorders can write x₁ as well as x₂. Consumerrecorders can write x₂ but on recordable discs, x₁ has a default valuex₁=x_c prepressed on the disc. The consumer recorder embeds watermarky=F(x_c||x₂) where x₂ is generated from a seed u, i.e., by taking aportion of the bits of G(u). The owner can copy his own creationsbecause he knows u. In players, neither x₁ nor x₂ leaves the basicengine, so it remains hidden for the user.

For the above embodiment, a suitable relation between the watermarkbitpattern and the medium mark bitpattern is a one-way function. Animplementation of the one-way function can be y=x² mod N with N a publicmodulus. Here N is the product of two secret large primes (N=pq). Infact N can be part of the data that is embedded in the watermark, i.e.,concatenated to y. Another possibility is the discrete-log one-wayfunction conjectured by Diffie and Hellman [1976] (=document D6 listedabove): F(x)=α^(x) in GF(p) with α a primitive element of GF(p). Here pis a large prime such that p−1 has a large prime factor. The above twoimplementations bear the disadvantage that the size of the arguments,i.e., the number of bits needed to be secure, is quite large. Apractical system based on fewer bits can be to apply an appropriatesecret-key encryption algorithm, e.g. the DES, with y=F(x)=x{circlearound (x)}DES(x). This is illustrated in the circuit of FIG. 3. FIG. 3shows an implementation of a one-way function generator based onsecret-key encryption algorithm. On the input 31 the medium markbitpattern x is applied and processed in the encryptor 32 by using a keyfrom a key input 33. The output of encryptor 32 is bitwise EXOR'd withthe input x by logic unit 34, resulting in bitpattern y on the output35. In this circuit, the key can be made public or included in thewatermark, i.e. concatenated to y.

FIG. 4 shows a recorder for consumers. The recorder has an analog audioinput 41 connected to an encoder 42 for DSD or PCM audio encoding, whichencoder produces at the output a bitstream 47 to be recorded onrecordable disc 48. The encoder 42 embeds a watermark bitpattern y inthe bitstream 47. The bitpattern y is created by generator 43 from abitpattern x, whereas x is to be represented by a medium mark 46 and mayinclude a number of bits derived from a prepressed physical mark on therecordable disc 48. The recorder has a seed input 45 for a seed uconnected to a generator 44 for generating the bitpattern x. Therecorder has a second input 40 for a digital audio signal connected to awatermark checker 40. The checker 49 is also connected to generator 43,for receiving bitpattern y and verifies the presence of a watermark. Thebasic recording control function of the checker is to block recording ifa professional “no-copy” watermark is detected. Preferably, a watermarkis present indicative of copyable content, a recording can be made onlyif the corresponding seed u is applied to the seed input 45. In adifferent embodiment, the consumer recorder only has the digital input40 and the watermark checker 49, whereas the analog input and watermarkencoder are not present. Further embodiments of the recorder are equalto the above but are not provided with an external input 45, but have aninternal generator for u, e.g. a random number generator. In that casealso generator 44 may not be present.

In its pure form, a conditional recording scenario does not performchecks during playback. In a different embodiment the consumer DSDrecorder accepts an analog signal, possibly conditional to some analogcopy information check. The on-board DSD encoder embeds a watermark intothe stream. This mark consists of two parts: copy protection data and aserial id. number of the recorder. The consumer DSD recorder accepts adigital DSD stream only if it can recognize valid copy control data.This copy control data should state that this material may legally becopied onto a disc. Such a recorder is similar to the recorder shown inFIG. 4, but does not have the seed input 45 and generator 44.

The consumer DSD recorder does not accept a DSD stream that containsCopy Control Marks that prohibit recording. In an embodiment of a strongform, the absence of Copy Control Information is interpreted as “no copyallowed”. In a weaker form, signals without copy control information areautomatically resampled and watermarked. This weakens the copyprotection, but leads to some quality degradation.

In a further embodiment a copy once feature is included. A professionalDSD stream contains embedded copy-right data that grants permission tocopy once. This can be implemented by embedding a further watermarky_(co) (in addition to mark described earlier). Moreover theprofessional disc contains a special permission mark x_(co) wherey_(co)=H(x_(co)) with H( ) a cryptographic one-way function. The marky_(co) remains with the audio (possibly embedded) during playback, butit is removed by the consumer recorder.

FIG. 5 shows a player 52 for reproducing information from a copyprotected information carrier 51. The player is provided with a readhead 58 and read signal processing apparatus of a usual type, such as anoptical head, a detector, a channel decoder and an error decoder of a CDor DVD optical disc player. The player includes watermark read detector55 for detecting a bitpattern y represented by the watermark in therecorded information on the information carrier 51. The bitpattern y iscoupled to a logic unit 54, which operates the enabling switch 56. Thelogic function of unit 54 has been discussed with reference to FIG. 1and the conditional playback rules. The player is provided with mediamark read detector 50 for detecting the medium mark and deriving thebitpattern x from the medium mark, e.g. by demodulating the wobblemodulation as known from document D1 listed above. The player isprovided with a verifier for verifying a predefined relationship betweenthe bitpattern x and the bitpattern y. In the verifier, the bitpattern xis coupled to a function unit 53 for performing a predefined functionF(x), e.g. a one-way function. The output y′ of the function unit 53 iscoupled to logic unit 54 and compared to y. The enabling switch 56passes the recovered audio signal to the output 57 if the bitpatterns xand y do show the predefined relationship.

It is noted that, hybrid solutions using conditional recording andconditional playback can co-exist. Of particular interest is a scenarioin which (despite technical difficulties described in the introduction)a watermark check in the analog domain should be performed by recorders.If a pirate manages to modify his recorder to bypass this conditionalrecording check, and put professional DSD on a disc anyhow, the copyprotection schemes described here can prevent playback on players in themarket.

Although the invention has been explained mostly by embodiments usingDSD audio, several embodiments of the watermarking of audio and/or videocan be used. Watermarking is also possible for PCM audio. An example ishiding data in the LSB's, possibly including a spectral shaping of theireffect. An implementation for such embedding scheme has been presentedby Oomen et al. in 1994 (see document D4 listed above). For ourapplication, we preferably would only embed data in a limited number ofpreselected samples, with one bit per selected sample. Such embeddingscheme can be implemented within the same device that convertsprofessional (24 bit) audio into lower resolution (e.g. 16 bits) Themethod previously mentioned for DSD watermarking (in document D3 listedabove) may also be used for embedding data in PCM. Another option is touse the loss-less encoding for embedded signaling. One method forlossless encoding was proposed by Bruekers et al (described in documentD5 listed above) A possible method of embedding data is by choosing theproperties or parameters of the predictive filter (FIG. 10, item 152 indocument D5 listed above) in accordance with watermarking rules. Forinstance, a digital watermark “1” can be represented by choosing an evennumber of filter taps and a “0” is represented by an odd number of taps.In another implementation, the filter coefficients are quantizedaccording to a similar rule. Further, the entropy encoder can embed databy adapting its parameters. Such signals embedded into the PCM signalcan be used to build a copy protection scheme based on any of thepreviously mentioned concepts. A pirate can no longer copy thecompressed PCM bit-by-bit onto a disc that he can distributecommercially. He must go through the process of decompression andcompression. Although this does not lead to a degradation in quality(because the coding is loss-less), it results in a different digitalsignal, the resulting file will contain more bits if consumer recorderscan compress less efficiently and the resulting file will containinformation about the serial number of the recorder.

In the embodiments a disc has been described as information carrier, butany other carrier can be used in the invention, such a tape orbroadcast, as long as the medium mark is supplied in a way which cannotbe easily copied. Further the invention lies in each and every novelfeature or combination of features.

1. A system comprising: a recorder, including: reading means for readingfrom an information carrier, a content of a medium mark, said contentcomprising a first bitpattern; generating means for generating a secondbitpattern according to a predefined relationship of with the firstbitpattern; encoder means for embedding a watermark containing thesecond bitpattern in user information to be recorded; and recordingmeans for recording the watermarked user information on the informationcarrier for storage, wherein the medium mark is contained in a wobble ofa track of the information carrier, the wobble representing the firstbit pattern; the system further comprising: a player including: firstreading means for reading the content of the medium mark, said contentcomprising the first bitpattern; second reading means for reading theembedded watermark containing the second bitpattern from the userinformation; verifying means for establishing a verification of therelationship between the second bit pattern and the first bit pattern;and enabling means for enabling playback of the recorded watermarkeduser information from the information carrier based on saidverification.
 2. The system of claim 1, in which the relationshipincludes a cryptographic function.
 3. The system of claim 2, in whichthe relationship includes a one-way function.
 4. The system of claim 1,in which the second bitpattern identifies the encoder means.
 5. 6. Thesystem of claim 1 in which the medium mark is pressed in the informationcarrier during manufacture.
 7. The system of claim 1 in which thewatermarked user information is stored on the information carrier in adifferent manner than the medium mark is stored, the user informationwriting means being insufficient for writing the medium mark on theinformation carrier.
 8. The system of claim 1, wherein said enablingmeans comprises an enabling switch.
 9. A recorder comprising: readingmeans for reading from an information carrier, a content of a mediummark, said content comprising a first bitpattern; generating means forgenerating a second bitpattern according to a predefined relationshipwith the first bitpattern; and encoder means for embedding a water markcontaining the second bitpattern in user information to be recorded; andrecording means for recording the watermarked user information in theinformation carrier for storage, in which the medium mark is containedin a wobble of a track of the information carrier, the wobblerepresenting the first bit pattern.
 10. The recorder of claim 9, inwhich: the recorder further comprises marking means for writing themedium mark on the information carrier; and the generating meansgenerate the first bitpattern from a seed according to a furtherpredefined relationship.
 11. The recorder of claim 10, in which thegenerating means generate the first bitpattern by combining a first partrepresented by a prepressed mark on a recordable information carrier anda second part generated from the seed.
 12. The recorder of claim 10, inwhich the further predefined relationship includes a cryptographicone-way function.
 13. The recorder of claim 9, in which: the recorderfurther comprises means for reading the first bitpattern from theinformation carrier; the first bit pattern indicates a copy protectionstatus of the information carrier; the relationship includes acryptographic function; the relationship includes a one-way function;the second bitpattern identifies the encoder means; the recorder furthercomprises marking means for writing the medium mark on the informationcarrier; the generating means generate the first bitpattern from a seedaccording to a further predefined relationship; and the generating meansare arranged for generating the first bitpattern by combining a firstpart represented by a prepressed mark on the information carrier and asecond part generated from a seed.
 14. An information carriercomprising: a medium mark, wherein a content of said medium markcomprises a first bitpattern, in which the medium mark is contained in awobble of a track of the information carrier, the wobble representingthe first bit pattern; and recorded user information encoded with awatermark containing a second bitpattern different from the first bitpattern and having a predefined relationship with the first bitpatternwhereby the relationship between the second bitpattern and the contentof the first bitpattern can be verified in a computer process.
 15. Theinformation carrier of claim 14, in which the first bitpattern includes:a first part identifying a source of the information carrier; and asecond part identifying the recorded information.
 16. The informationcarrier of claim 14, in which: the relationship includes a cryptographicfunction; the relationship includes a one-way function; and the secondbitpattern identifies encoded user information.
 17. A player for aninformation carrier comprising: first reading means for reading acontent of a medium mark, said content comprising a first bitpattern, inwhich the medium mark is contained in a wobble of a track of theinformation carrier, the wobble representing the first bit pattern;second reading means for reading an embedded watermark containing asecond bitpattern from recorded user information; verifying means forverifying a predefined relationship between the second bitpattern andthe first bitpattern; and enabling means for enabling playback ofrecorded user information from the information carrier based on saidpredefined relationship.
 18. The player of claim 17, in which theverifying means includes a cryptographic one-way function.
 19. Theplayer of claim 18, in which: the verification means generate averification pattern by applying a one-way function to the firstbitpattern; and the verifying means compare the verification pattern andthe second bitpattern in order to verify the predefined relationship.20. The player of claim 18, in which: the relationship includes acryptographic one-way function; the relationship includes a one-wayfunction; and the second bitpattern identifies the predefinedrelationship.
 21. The player of claim 17, wherein said enabling meanscomprises an enabling switch.
 22. A system for copy protection ofinformation recorded on an information carrier, the system comprising: amedium mark on the information carrier containing a first bitpattern,wherein the medium mark is contained in a wobble of a track of theinformation carrier, the wobble representing the first bit pattern, arecorder for embedding a watermark into a set of information data andfor recording a watermarked set of information data on the informationcarrier, the watermark containing a second bit pattern having apredefined relationship to the first bitpattern, and a player forverifying the relationship between the first bit pattern and the secondbit pattern and for reproducing the watermarked set of information fromthe information carrier.
 23. The system of claim 22, wherein thepredefined relationship comprises a cryptographic one-way function. 24.The system of claim 23, wherein the second bitpattern is generated byapplying a one-way function to the first bitpattern.
 25. The system ofclaim 22, wherein the recorder comprises encoding means for encoding aunique seed on the information carrier allowing the encoding means to beidentified from the second bitpattern.
 26. A recorder for recordinginformation on an information carrier containing a medium mark, contentsof the medium mark containing a first bit pattern, the recordercomprising: generator means for generating a second bitpattern accordingto a predefined relationship between the first bit pattern and thesecond bitpattern, wherein the medium mark is contained in a wobble of atrack of the information carrier, the wobble representing the first bitpattern, encoder means for embedding a watermark in the information, thewatermark containing the second bitpattern, and means for recordingwatermarked information on the information carrier containing the mediummark.
 27. The recorder of claim 26, wherein the recorder furthercomprises marking means for generating the first bitpattern from a seedaccording to a further predefined relationship and for providing themedium mark on the information carrier.
 28. The recorder of claim 27,wherein the further predefined relationship includes a cryptographicone-way function.
 29. The recorder of claim 26, wherein the generatormeans are arranged for generating the first bitpattern by combining afirst part represented by contents of a prepressed mark on a recordableinformation carrier and a second part generated from a seed.
 30. Therecorder of claim 26 further comprising further encoding means forcryptographically scrambling the watermarked information using the firstbit pattern before the watermarked information is recorded so thatrecorded information is scrambled.
 31. The recorder of claim 26, whereinthe recorder further comprises means for reading the medium mark fromthe information carrier.
 32. The recorder of claim 26 wherein therecorder manufacturers a disk by pressing.
 33. An information carriercomprising: recorded information, and a medium mark, contents of themedium mark containing a first bitpattern and wherein the medium mark iscontained in a wobble of a track of the information carrier, the wobblerepresenting the first bit pattern, the recorded information including awatermark containing a second bitpattern different from the first bitpattern and having a predefined relationship to the first bitpattern.34. The information carrier of claim 33, wherein the first bitpatternincludes a first part identifying a source of the information carrier,and a second part identifying the recorded information.
 35. A player forreproducing information from an information carrier and comprising:means for reading a medium mark from the information carrier, contentsof the medium mark containing a first bitpattern, wherein the mediummark is contained in a wobble of a track of the information carrier, thewobble representing the first bit pattern, means for recovering awatermark from information read from the information carrier, thewatermark containing a second bitpattern, and verification means forverifying a predefined relationship between the second bitpattern andthe first bitpattern, and means for reproducing information containingthe watermark from the information carrier.
 36. The player of claim 35,wherein the verification uses a cryptographic one-way function.
 37. Theplayer of claim 35, wherein the verifications means are arranged forgenerating a verification pattern by applying a one-way function to thefirst bitpattern and for comparing the verification pattern and thesecond bitpattern.
 38. The player of claim 35 wherein reproduction ofinformation by the player is dependent upon the predeterminedrelationship as verified by the verification means.
 39. A system forcopying protection of information recorded on an information carrier,the system comprising: a medium mark on the information carriercontaining a first bitpattern, a recorder for embedding a watermark intoa set of information data and for recording a watermarked set ofinformation data on the information carrier, the watermark representinga second bit pattern having a predefined relationship to the firstbitpattern, and a player for verifying the relationship between thefirst bit pattern and the second bit pattern and for reproducing thewatermarked set of information from the information carrier, wherein thefirst bit pattern is a cryptographic key for de-scrambling recordedinformation to recover the watermarked information, and the second bitpattern is recovered from the watermark of the watermarked information.40. A recorder for recording information on a record carrier,comprising: means for reading a medium mark from the record carrier,contents of the medium mark containing a first bitpattern, wherein themedium mark is contained in a wobble of a track of the informationcarrier, the wobble representing the first bit pattern; means fordetermining whether the information contains a watermark containing asecond bitpattern that has a predetermined relationship with the firstbit pattern; and means for recording information dependent upon resultof the means for determining.
 41. The recorder of claim 40 wherein themeans for determining further identifies a verification pattern byapplying a one-way function to the first bitpattern and comparing theverification pattern and the second bitpattern.
 42. A system comprising:a recorder, including: reading means for reading from an informationcarrier, a content of a medium mark, said content comprising a firstbitpattern; generating means for generating a second bitpatternaccording to a predefined relationship of with the first bitpattern;encoder means for embedding a watermark representing the secondbitpattern in user information to be recorded, wherein the first bitpattern is a cryptographic key for de-scrambling recorded information torecover the watermarked information, and the second bit pattern isrecovered from the watermark of the watermarked information; andrecording means for recording the watermarked user information on theinformation carrier for storage; the system further comprising: a playerincluding: first reading means for reading the content of the mediummark, said content comprising the first bitpattern; second reading meansfor reading the embedded watermark representing the second bitpatternfrom the user information; verifying means for establishing averification of the relationship between the second bit pattern and thefirst bit pattern; and enabling means for enabling playback of therecorded watermarked user information from the information carrier basedon said verification.
 43. A recorder comprising: reading means forreading from an information carrier, a content of a medium mark, saidcontent comprising a first bitpattern; generating means for generating asecond bitpattern according to a predefined relationship with the firstbitpattern; and encoder means for embedding a watermark representing thesecond bitpattern in user information to be recorded; and recordingmeans for recording the watermarked user information in the informationcarrier for storage, wherein the first bit pattern is a cryptographickey for de-scrambling recorded information to recover the watermarkedinformation, and the second bit pattern is recovered from the watermarkof the watermarked information.
 44. An information carrier comprising: amedium mark, wherein a content of said medium mark comprises a firstbitpattern, and wherein the medium mark is contained in a wobble of atrack of the information carrier, the wobble representing the first bitpattern; and recorded user information encoded with a watermarkcontaining a second bitpattern different from the first bit pattern andhaving a predefined relationship with the first bitpattern whereby therelationship between the second bitpattern and the content of the firstbitpattern can be verified in a computer process, wherein the first bitpattern is a cryptographic key for de-scrambling recorded information torecover the watermarked information, and the second bit pattern isrecovered from the watermark of the watermarked information.
 45. Aplayer for an information carrier comprising: first reading means forreading a content of a medium mark, said content comprising a firstbitpattern; second reading means for reading an embedded watermarkrepresenting a second bitpattern from recorded user information, whereinthe first bit pattern is a cryptographic key for de-scrambling recordedinformation to recover watermarked information, and the second bitpattern is recovered from the watermark of watermarked information;verifying means for verifying a predefined relationship between thesecond bitpattern and the first bitpattern; and enabling means forenabling playback of recorded user information from the informationcarrier based on said predefined relationship.
 46. A recorder forrecording information on an information carrier containing a mediummark, contents of the medium mark representing a first bit pattern, therecorder comprising: generator means for generating a second bitpatternaccording to a predefined relationship between the first bit pattern andthe second bitpattern, encoder means for embedding a watermark in theinformation carrier, the watermark representing the second bitpattern,and means for recording watermarked information on the informationcarrier containing the medium mark, wherein the first bit pattern is akey for de-scrambling recorded information to recover watermarkedinformation, and the second bit pattern is recovered from the watermarkof watermarked information.
 47. An information carrier comprising:recorded information, and a medium mark, contents of the medium markcontaining a first bitpattern wherein the medium mark is contained in awobble of a track of the information carrier, the wobble representingthe first bit pattern, the recorded information including a watermarkcontaining a second bitpattern different from the first bit pattern andhaving a predefined relationship to the first bitpattern, wherein thefirst bit pattern is a cryptographic key for de-scrambling recordedinformation to recover watermarked information, and the second bitpattern is recovered from the watermark of watermarked information. 48.A player for reproducing information from an information carrier andcomprising: means for reading a medium mark from the informationcarrier, contents of the medium mark representing a first bitpattern,means for recovering a watermark from information read from theinformation carrier, the watermark representing a second bitpattern, andverification means for verifying a predefined relationship between thesecond bitpattern and the first bitpattern, and means for reproducinginformation containing the watermark from the information carrier,wherein the first bit pattern is a cryptographic key for de-scramblingrecorded information to recover watermarked information, and the secondbit pattern is recovered from the watermark of watermarked information.